EvidenceSheet
NIST SP 800-53 Rev 5 · AC - Access Control

AC-21 Information Sharing

a. Enable authorized users to determine whether access authorizations assigned to a sharing partner match the information’s access and use restrictions for organization-defined information sharing circumstances where user discretion is required; and b. Employ organization-defined automated mechanisms or manual processes to assist users in making information sharing and collaboration decisions.

Source: NIST SP 800-53 Rev 5, AC-21. The statement above is our statement of the clause, read from the published text and cited so you can check it against the official text, not the instrument verbatim. Open NIST SP 800-53 Rev 5 in the compliance library.

Base controls and their enhancements. Which apply follows the baseline you are assessed against (for example FedRAMP Moderate or High, or the low, moderate and high baselines of SP 800-53B). Text in square brackets is a parameter your organisation sets.

10
artefacts
3
held by a system
0
at each review
moderate
to go live
Identity provider / directory
where the evidence lives
teal = a system already holds it · olive = produced at each review. To go live: easy when half or more of the artefacts are already held by a system, moderate from a quarter to a half, hard below a quarter.

These are the artefacts auditors commonly ask for on this requirement, our guidance rather than text from the standard. Your assessor decides what is sufficient in your context, and asks for samples across the period when a report covers one.

system holds itEvidence a system already holds

  • List of users authorized to make information-sharing/collaboration decisions · Identity provider / directory
  • List of information-sharing circumstances requiring user discretion · Identity provider / directory
  • Test of Automated mechanisms or manual process implementing access authorizations supporting information-sharing/user collaboration decisions · Identity provider / directory

periodic reviewEvidence produced at each review

none for this control

governing documentDocuments that govern the control

  • Access control policy · Policy repository / GRC workspace
  • Procedures addressing user-based collaboration and information sharing (including restrictions) · Policy repository / GRC workspace
  • System design documentation · Policy repository / GRC workspace
  • System configuration settings and associated documentation · Policy repository / GRC workspace
  • Non-disclosure agreements · Policy repository / GRC workspace
  • Acquisitions/contractual agreements · Policy repository / GRC workspace
  • System security plan · Policy repository / GRC workspace

First move

Start with the 3 of 10 artefacts that already live in a system (Identity provider / directory); keep the periodic reviews but log each one as a dated record with a named reviewer.

Common gaps auditors find

Do this for your whole sheet

Paste the rows you run your controls from and get this mapping for every control at once, with the periodic-review ones flagged and a first move per row. No account for the first run.

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AC-20(5) Use of External Systems | Portable Storage Devices: Prohibited Use · AC-21(1) Information Sharing | Automated Decision Support